Synchronous rectifiers provide an efficient way of generating the required low operating voltages and high currents for electronic devices such as power supplies for laptop computers. Synchronous rectifiers are used in a variety of topologies, including forward converters, flyback converters, buck converters, push-pull converters, and half-bridge converters, inductor-inductor-capacitor (LLC) converters, and the like. For example in an LLC flyback converter employing a synchronous rectifier, a power transistor replaces a secondary side diode to obtain a lower on-state voltage drop. The synchronous rectifier uses a metal-oxide-semiconductor field effect transistor (MOSFET) rather than a diode to avoid the turn on voltage drop of a diode, which can decrease converter efficiency. For example, an N-channel MOSFET synchronous rectifier is biased to conduct from source-to-drain when a diode would have been conducting from anode to cathode, and conversely, is made nonconductive to block voltage from drain-to-source when a diode would have been blocking from cathode to anode. To decrease on resistance, the MOSFET is made large, which increases the energy required to charge and discharge the gate.
The use of the same reference symbols in different drawings indicates similar or identical items.